The carbide chamber _D_ has at its bottom a conical valve,
normally open, but closed by means of the spindle _H_, which is
engaged at its upper end by the closing screw-cap _J_, which is
furnished with a safelocking device to prevent its removal until the
conical valve is closed and the hopper chamber _D_ thereby cut off
from the gas-supply. The cap _J_, in addition to a leather washer to
make a gas-tight joint when down, has a lower part fitting to make an
almost gas-tight joint. Thus when the cap is off; the conical valve fits
gas-tight; when it is on and screwed down it is gas-tight; and when on
but not screwed down, it is almost gas-tight. Escape of gas is thus
avoided. A special charging funnel _K_, shown in half-scale, is
provided for inserting in place of the screw cap. The carbide falls from
the funnel into the chamber _D_ when the chain is pulled. A fresh
charge of carbide may be put in while the apparatus is in action. The
evolved gas goes into the chamber _C_ through a pipe, with cock, to
a dust-arrester _L_, which contains a knitted stocking lightly
filled with raw sheep's wool through which the gas passes to the service-
pipe. The dust-arrester needs its contents renewing once in one, two, or
three years, according to the make of gas.
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